Apparatus and method for detecting defect signals

ABSTRACT

The method of detecting defect signals includes: setting a default pit length range; inputting a data signal including a plurality of pits with different pit lengths; transferring the data signal into NRZ signal and counting the pit length of each pit; accumulating the number of the pits whose pit length are within the default pit length range, and accumulating the number of the pits whose pit lengths are outside the default pit length range but within the corresponding ranges; changing the logic state of a defect flag signal when one of the accumulative value reaches a corresponding threshold. The present invention also provides an apparatus for detecting defect signals.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and apparatus for detecting datasignals in an optical disk system, and more particularly to a method andapparatus for detecting defect signals in an optical disk system.

2. Discription of the Prior Art

Because of the invention of the optical storage media, it is notdifficult to store massive data. And because the optical storage mediastore data by recording data in the optical storage media in a digitalway, data can be stored in a longer time compared with the conventionalmagnetic media in an analog way. In the meantime, the data will not bedistorted with the time passing.

The earliest specification (red book) of the optical storage media wasaccomplished by Philip and Sony at 1980. Thereafter, many otherspecifications (e.g. yellow book, orange book . . . ) were finished foraccommodating different contents. But basically, the storing formats ofthe optical storage media are the same, and they are expanded inaccordance with the red book.

The data signal has to be modulated before stored in the optical storagemedia. For compact disk (CD), the data signal is processed in Eight toFourteen Modulation (EFM) first. The modulated signal is a series ofbinary signals with the combination of logic “1” and logic “0”. If thebinary signals are written into the CD directly, the pickup head of theoptical storage media can not read the logic level states of every bitprecisely, because the lengths of the binary pits are just about 0.13um-0.15 um. Therefore, the modulated data signals have to be coded inthe different lengths of pits (or lands) with lengths of 3T to 11T (3T,4T, 5T, 6T, 7T, 8T, 9T, 10T, and 11T)(as shown in FIG. 1A), and storedin the optical storage media. The coding method of 3T to 11T is socalled (2,10) RLL (Run Length Limited) coding (as shown in FIG. 1B).That means the data tracks of the optical disks are made of the helicaltracks of pits with 9 different lengths. As shown in FIG. 2, 2A is apiece of data signal of the data track in an optical disk. RF signal 2Bis reflected from the pickup head by tracking the data signals of thedata track, while 2C is the NRZ signal corresponding to 2A in the (2,10)RLL coding. Because the reflected RF signal caused by the pits withdifferent lengths has different signal amplitude intensities, the systemcan identify every data signal in accordance with its amplitudeintensity. When the logic level of the NRZ signal in 2C changes (fromthe logic high level to logic low level, or from the logic low level tologic high level), it indicates logic “1”. When the logic level keepsthe same, it indicates logic “0”.

Similarly, DVD (digital versatile disk) adopts the same method. The datasignal is processed in 8 to 16 modulation (EFM plus), which are coded in3T to 11T respectively and plus a 14T component, then the pits withdifferent lengths are formed and stored in a DVD. For an optical disk,there is a plastic layer on its surface for protection, but it is likelyto have defect signals produced by scratches or some exterior factors,such as the process of recording, fingerprints . . . etc. The defectsignals cause the pickup head not to reflect the correct RF signals whentracking. Therefore, the optical disk system cannot read out the neededdata signals and then cause false movements.

The RF signals produce irregular variation because of the existingdefect signals. The conventional way of detecting defect signals is asshown in FIG. 3 which adds the reference voltage level 3B to the RFsignals 3A reflected from data signals. When the voltage level of theenvelope signal 3C of the RF signal 3A is lower than the referencevoltage level 3B (as shown in the 3E area of FIG. 3), the defect flagsignal 3D arises from the logic low level to logic high level to denotethe 3E area has a defect signal, and inform the servo system of theoptical disk system not to lock frequency to prevent from making amistake.

But when the defect signals of the optical disk are not serious (e.g.defects caused by scratches and fingerprints), if the method describedabove is still adopted, it is possible the location of the defect signalcannot be found by the reflected RF signal from the data signal, asshown in FIG. 4. The voltage level of the defect portion in the envelopesignal 4C of the RF signal 4A (as shown in 4E area of FIG. 4) is higherthan the reference voltage level 4B in contrast. Thereby, the locationof the defect signal cannot be found by the reflected RF signal from thedata signal, and the defect flag signal 4D cannot reflect the appearanceof the defect signal correctly.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for detectingdefect signals to make the optical disk system be able to correctlyidentify the portion of the optical disk with defect signals to preventthe optical disk system from generating false movements because of thedata signal reading with defects.

The apparatus for detecting defect signals of the present inventionincludes: a buffering memory for storing data signals of the opticaldisk wherein every data signal includes a plurality of pits withdifferent lengths; a first counter for counting the length of each pit;a second counter for accumulating the number of the pits whose pitlengths are within a default pit length range and comparing theaccumulated number with the corresponding default threshold; a thirdcounting unit including a plurality of the third counters; and a defectsignal detecting circuit for generating a defect flag signal and changeits logic level in accordance with the result of the comparison bycomparing the accumulated numbers of the second counter and a pluralityof the third counters with the corresponding thresholds. Therein, eachof the third counters includes a corresponding range of the pit length,and accumulates the number of the pits whose pit lengths are bothoutside the default pit length range and within each of thecorresponding range of the pit length respectively. In the meantime,each of the third counters has a corresponding default threshold to becompared with the corresponding accumulated numbers respectively.

The method for detecting defect signals of the present inventionincludes: setting a default pit length range; inputting a batch of datasignals including a plurality of pits with different lengths; convertingthe data signals into the NRZ signals and counting the pit length ofeach pit in the data signals respectively; and accumulating the numbersof the pits whose pit lengths are within or outside the default pitlength range and triggering a defect flag signal as a logic high levelor logic low level when one of the accumulated numbers reaches thecorresponding default threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is the diagram of pit length.

FIG. 1B is the diagram of pit length.

FIG. 2 is the diagram of the data signals of an optical disk.

FIG. 3 is the diagram of a prior art for detecting defect signals.

FIG. 4 is the diagram of another prior art for detecting defect signals.

FIG. 5 is the apparatus for detecting defect signals of the presentinvention.

FIG. 6 is the flow chart for detecting defect signals of the presentinvention.

FIG. 7 is the apparatus of the present invention applied in the readingof an optical disk.

FIG. 8 is the flow chart of the present invention applied in the readingof an optical disk.

FIG. 9 is the signal diagram of the present invention applied in thereading of an optical disk.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides an apparatus and method for detectingdefect signals which can make the optical disk system to detect thedefect signals of the optical disk correctly. The following illustratesthe preferred embodiment of the present invention. But the skilled inthe art should understand that is only an illustration and not to limitthe present invention itself. The preferred embodiment of the presentinvention is described as follows.

As shown in FIG. 5, the apparatus for detecting defect signals of thepresent invention 500 includes: a buffering memory 510, a first counter520, a second counter 530, a third counting unit 540, and a defectsignal detecting circuit 550. The buffering memory 510 stores the datasignals of the optical disk, wherein every data signal includes aplurality of pits with different lengths. The first counter 520 couplesto the buffering memory 510 for counting the length of each pit. Thesecond counter 530 couples to the first counter for accumulating thenumber, counted by the first counter, of the pits whose pit lengths arewithin a default pit length range each time, and compare the accumulatednumber CNT2 with the corresponding default threshold SHR2. The thirdcounting unit includes a plurality of the third counters (540_1, 540_2 .. . ) and couples to the first counter 520. Each of the third counters(540_1, 540_2 . . . ) includes a corresponding pit length range outsidethe default pit length range respectively to accumulate the numberswithin the corresponding pit length (CNT3_1, CNT3_2 . . . )respectively. In the meantime, each of the third counters (540_1, 540_2. . . ) includes a corresponding default threshold (SHR3_1, SHR3_2 . . .) respectively to be compared with the corresponding accumulated number(CNT3_1, CNT3_2 . . . ) respectively. The defect signal detectingcircuit 550 generates a defect flag signal DEF_FLAG set at the firstlogic level. The defect flag signal DEF_FLAG changes its logic level inaccordance with the result of the comparison by comparing theaccumulated numbers CNT2, (CNT3_1, CNT3_2 . . . ) of the second counter530 and the third counting unit 540 with the corresponding defaultthresholds SHR2, (SHR3_1, SHR3_2 . . . ). In another word, the logiclevel of the defect flag signal DEF_FLAG becomes the second logic level(assumed as the high logic level, the logic 1), if the logic level ofthe defect flag signal DEF_FLAG is the default first logic level(assumed as the low logic level, the logic 0) and a defect signal isidentified.

The method for detecting defect signals of the present inventionincludes the follows. A default pit length range is set. Then, a batchof the data signals D(P₀, P₁, P₂ . . . P_(N-1)) are input to thebuffering memory 510, and the batch of the signals D(P₀, P₁, P₂ . . .P_(N-1)) includes N pits. A defect flag signal DEF_FLAG is set toindicate if the batch of the signals D(P₀, P₁, P₂ . . . P_(N-1)) includeany defect signal or not, while the default of the defect flag signalDEF_FLAG is maintained at the first logic level (when there is no defectsignal). The data signals with N different pits are converted into theNRZ signals, and then each pit length (L₀, L₁, L₂ . . . L_(N-1)) iscounted by the first counter in the order of the pits, and then outputto the counter with the corresponding range in accordance with thecounted result. The second counter 530 is employed to accumulate thenumbers CNT2 of the pits whose pit lengths are within the default pitlength range, or each of the third counters (540_1, 540_2 . . . ) of thethird counting unit 540 is employed to accumulate the number of the pitswhose pit lengths are outside the default pit length range and thenumber (CNT3_1, CNT3_2 . . . ) of the corresponding range of the pitlength for each of the third counters (540_1, 540_2 . . . ). Theaccumulated numbers CNT2 and (CNT3_1, CNT3_2 . . . ) and the defaultthresholds SHR2 and (SHR3_1, SHR3_2 . . . ) are compared each time. Whenthe accumulated numbers reach the default thresholds, the logic level ofthe defect flag signal DEF_FLAG is changed (If being the first logiclevel, the logic level of the defect flag signal DEF_FLAG is changed tothe second logic level; in contrast, if being the second logic level,the logic level of the defect flag signal DEF_FLAG is changed to thefirst logic level). When counting each of the pit lengths of the datasignals is finished, all of the accumulated numbers of the counters arereset.

When detecting the logic level of the defect flag signal DEF_FLAG ischanged, the optical disk servo system controls whether to lockfrequency in accordance with the state of the logic level (If the defectflag signal DEF_FLAG is at the default first logic level, the opticaldisk servo system locks frequency; in contrast, if the defect flagsignal DEF_FLAG is at the second logic level, the optical disk servosystem does not lock frequency).

It is noted the accumulated number CNT2 is the number of the accumulatedpits whose pit lengths are within the default pit length range. Theresult of the comparison of the accumulated numbers CNT2 and the defaultthreshold SHR2 can work as the standard about whether the defect flagsignal DEF_FLAG returns to the default first logic level from the secondlogic level to indicate there is no defect signal in the portion of theof the data signals D(P₀, P₁, P₂ . . . P_(N-1)). If the defect flagsignal DEF_FLAG has been at the default first logic level, the logiclevel of defect flag signal DEF_FLAG remains at the default first logiclevel even the accumulated number CNT2 reaches the default thresholdSH2.

It is also noted the accumulated numbers (CNT3_1, CNT3_2 . . . ) are thenumbers when that the pit lengths of the accumulated pits are outsidethe default pit length range (such as bigger than the default pit lengthrange, or smaller than the default pit length range) happens. The resultof the comparison of the accumulated numbers (CNT3_1, CNT3_2 . . . ) andthe default thresholds (SHR3_1, SHR3_2 . . . ) can work as the standardabout whether the defect flag signal DEF_FLAG returns to the secondlogic level from the default first logic level to indicate there aredefect signals in the portion of the data signals D(P₀, P₁, P₂ . . .P_(N-1)). If the defect flag signal DEF_FLAG has been at second logiclevel, the logic level of defect flag signal DEF_FLAG remains at thesecond logic level even one of the accumulated numbers (CNT3_1, CNT3_2 .. . ) reaches the its corresponding default threshold (SHR3_1, SHR3_2 .. . ).

The method is shown as FIG. 6:

-   -   Set a default pit length range (610);    -   Input data signals D(P₀, P₁, P₂ . . . P_(N-1)) including a        plurality of pits (620);    -   Convert the data signals D(P₀, P₁, P₂ . . . P_(N-1)) into the        NRZ signals (630);    -   Set a defect flag signal DEF_FLAG at the first logic level        (640);    -   Set M=0, CNT2=0, CNT3=0 (CNT3_1, CNT3_2 . . . ) (642);    -   Count the length L_(M) of the Mth pit P_(M) (650);    -   Judge whether the defect flag signal DEF_FLAG is at the first        logic level; if yes, execute step 670, otherwise, execute step        680 (660);    -   Judge whether the pit length L_(M) is within the default pit        length range; if yes, execute step 690, otherwise, execute step        672 (670);    -   Find the counter (540_J) of the corresponding range of the pit        length L_(M) among the third counters (540_1, 540_2 . . . ), and        add 1 to the accumulated number CNT3_J of the third counter        540_J (CNT3_J=CNT3_J+1) (672);    -   Judge whether CNT3_J reaches the default threshold SHR3_J; if        yes, execute step 676, otherwise, execute step 690 (674);    -   The defect flag signal DEF_FLAG is pulled to the second logic        level, and jump to step 690 (676);    -   Judge whether the pit length L_(M) is within the default pit        length range; if yes, execute step 682, otherwise execute step        690 (680);    -   The accumulated number CNT2 of the second counter 530 is        CNT2=CNT2+1 (682);    -   Judge whether the accumulate number CNT2 reaches the default        threshold SHR2; if yes, execute step 686, otherwise, execute        step 690 (684);    -   The defect flag signal DEF_FLAG is pulled to the first logic        level, and jump to step 690 (686);    -   M=M+1, and return to step 650 (690);    -   Judge whether M is equal to N; if yes, execute step 694,        otherwise, execute step 692 (692); and    -   Reset all of the counters, and return to step 620 (694).

An example of an optical disk is described as following. The length ofevery frame signal of an optical disk is known to be 588T. The range ofevery pit length is from 3T to 11T. An optical disk servo system isillustrated. As mentioned above, the present invention is applied in anapparatus 700 of an optical disk servo system for detecting defectsignals, as shown in FIG. 7, including a first counter 720, a secondcounter 730, a third counting unit 740, and a defect signal detectingcircuit 750. The buffering memory 710 stores data signals D of theoptical disk, wherein every data signal D includes a plurality of pits(P₀, P₁, P₂ . . . P_(N-1)) with different lengths. The first counter 720couples to the buffering memory 710 for counting the length (L₀, L₁, L₂. . . L_(N-1)) of each pit (P₀, P₁, P₂ . . . P_(N-1)). The secondcounter 730 couples to the first counter 720 for accumulating thenumbers, counted by the first counter 720, of the pits whose pit lengths(L₀, L₁, L₂ . . . L_(N-1)) are within a default pit length range RANGE(3T-11T) of the pit length each time, and comparing the accumulatednumber CNT2 with the corresponding default threshold SHR2. The thirdcounting unit 740 includes three the third counters (740_1, 740_2,740_3) and respectively couples to the first counter 720. Each of thethird counters (740_1, 740_2, 740_3) includes a corresponding pit lengthrange outside the default pit length range RANGE (3T-11T) but within thecorresponding pit length (CNT3_1, CNT3_2 . . . ) respectively. Inanother word, The first the third counter 740_1 accumulates the numberCNT3_1 of the pits whose pit lengths (L₀, L₁, L₂ . . . L_(N-1)) aresmaller than the default pit length range RANGE (smaller than 3T). Thesecond the third counter 740_2 accumulates the number CNT3_2 of the pitswhose pit lengths (L₀, L₁, L₂ . . . L_(N-1)) are bigger than the defaultpit length range RANGE (bigger than 11T). The third the third counter740_2 accumulates the number CNT3_3 of the pits whose pit lengths (L₀,L₁, L₂ . . . L_(N-1)) are much bigger than the default pit length rangeRANGE (much bigger than 11T, such as 18T). Besides, each of the thirdcounters (740_1, 740_2, 740_3) includes a corresponding defaultthreshold (SHR3_1, SHR3_2, SHR3_3) respectively to be compared with thecorresponding accumulated number (CNT3_1, CNT3_2, CNT3_3) respectively.The defect signal detecting circuit 750 generates a defect flag signalDEF_FLAG set at the low logic level. The defect flag signal DEF_FLAGchanges the logic level of itself in accordance with the result of thecomparison by comparing the accumulated numbers CNT2, and (CNT3_1,CNT3_2 . . . ) of the second counter 730 and the third counting unit 740with the corresponding default threshold SHR2, and (SHR3_1, SRR3_2,SHR_3).

The method of the present invention applied on an optical disk servosystem for detecting defect signals of an optical disk is shown as FIG.8:

-   -   Set the default pit length range RANGE of the pit length as        3T-11T (810);    -   Input data signals D(P₀, P₁, P₂ . . . P_(N-1)) including a        plurality of pits (820);    -   Convert the data signals D(P₀, P₁, P₂ . . . P_(N-1)) into the        NRZ signals (830);    -   Set a defect flag signal DEF_FLAG at the low logic level (840);    -   Set M=0, CNT2=0, CNT3_1=0, CNT3_2=0, CNT3_3=0 (842);    -   Count the length L_(M) of the Mth pit P_(M) (850);    -   Judge whether the defect flag signal DEF_FLAG is at the low        logic level; if yes, execute step 870, otherwise, execute step        880 (860);    -   Judge whether the pit length L_(M) is within the default pit        length range RANGE (=3T-11T) of the pit length; if yes, execute        step 890, otherwise, execute step 871 (870);    -   Judge whether the pit length L_(M) is smaller than 3T; if yes,        execute step 872, otherwise execute step 874 (871);    -   The accumulated number CNT3_1 of the first the third counter        740_1 adds 1; in another word, CNT3_1=CNT3_1+1, and then execute        step 873 (872);    -   Judge whether CNT3_1 reaches the default threshold SHR3_1; if        yes, execute step 876, otherwise, execute step 890 (873);    -   Judge whether the pit length L_(M) is bigger than 18T; if yes,        execute step 875, otherwise, execute step 877 (874);    -   The accumulated number CNT3_3 of the third the third counter        740_1 adds 1; in another word, CNT3_3=CNT3_3+1, and then execute        step 876 (875);    -   Judge whether CNT3_3 reaches the default threshold SHR3; if yes,        execute step 879, otherwise, execute step 890 (876);    -   The accumulate number CNT3_2 of the second the third counter        740_3 adds 1, CNT3_2=CNT3_2+1, and then execute step 878 (877);    -   Judge whether CNT3_2 reaches the default threshold SHR2; if yes,        execute step 879, otherwise, execute step 890 (878);    -   The defect flag signal DEF_FLAG is pulled to the high logic        level, and then jump to step 890 (879);    -   Judge whether the pit length L_(M) is within the default pit        length range RANGE (=3T-11T) of the pit length; if yes, execute        step 882, otherwise execute step 890 (880);    -   The accumulated number CNT2 of the second counter 730 is        CNT2=CNT2+1 (882);    -   Judge whether the accumulate number CNT2 reaches the default        threshold SHR2; if yes, execute step 886, otherwise, execute        step 890 (884);    -   The defect flag signal DEF_FLAG is pulled to the low logic        level, and jump to step 890 (886);    -   M=M+1 (890);    -   Judge whether M is equal to N; if yes, execute step 894,        otherwise, execute step 850 (892); and    -   Reset all of the counters, and return to step 820 (894).

According to the mentioned above, as shown in FIG. 9, 9A is a datasignal with defect signals, 9B is the corresponding NRZ signal, and 9Cis the defect flag signal. When the defect flag signal 9C is at lowlogic level, only the number that the pits whose pit lengths are against3T-11T coding are counted. Therefore, if the number that the pits whosepit lengths are smaller than 3T or bigger than 11T in the area 9E reachthe default threshold SHR3_1 or SHR3_2, or when the pit length is biggerthan 18T even once, the defect flag signal DEF_FLAG is pulled to thehigh logic level to inform the optical disk servo system to stop lockingthe data signals (defect signals). Otherwise, when the defect flagsignal DEF_FLAG is at the low logic level, only the number that the pitswhose pit lengths fit the 3T-11T NRZ coding are counted. In anotherworld, when the accumulate numbers that the pits whose pit lengths fitthe 3T-11T NRZ coding reaches the default threshold SHR2 in 9F, thedefect flag signal DEF_FLAG is pulled from the high logic level to thelow logic level to inform the optical disk servo system to start lockingthe data signals.

Although there is a plastic layer covering an optical disk to protectthe data in the optical disk, it is unavoidable that the data in theoptical disk is possible to have defect data caused by unconsciousscratches or some other external facts. If the optical disk servo systemdoes not detect the defect signals correctly, it is possible to causemistakes when reading, or further cause fault movements of the opticaldisk servo system.

As the mentioned above, the present invention provides the apparatus andmethod for detecting defect signals so that the optical disk servosystem can judge whether there is any defect signal without the need toadopting the DC reference voltage externally. By adopting the apparatusand method for detecting defect signals of the present invention, theoptical disk servo system can identify where the defect signals are fastand efficiently to work as the authority on whether the optical diskservo system controls the lock-tracking.

Although the present invention is applied on the preferred embodimentsfor reading data signals in an optical disk of an optical disk servosystem, it does not mean to limit the spirit of the present inventionand also does not mean that the essence of the present invention canonly be applied on the embodiments mentioned above. It can cover anykind of data modes of optical disks, such as digital versatile opticaldisk data mode. The spirit of the present invention covers them all.Therefore, any modification without departing the spirit and scope ofthe present invention should all be included in the following claims.

1. A method for detecting defect signals, comprising: setting a defaultpit length range; inputting a data signal including a plurality of pits;transferring the data signal into a non-return to zero (NRZ) signal;counting a pit length of each of a plurality of the pits in an order ofa plurality of the pits each time; accumulating a first number of aplurality of the pits whose pit lengths are within the default pitlength range and accumulating a second number of a plurality of the pitswhose pit lengths are outside the default pit length range each time;and triggering a defect flag signal when the first number and the secondnumber reach a plurality of corresponding thresholds respectively,wherein a default level of the defect flag signal is set at a firstlogic level.
 2. The method for detecting defect signals according toclaim 1, wherein the defect flag signal is triggered to be at a secondlogic level when the first number reaches a first correspondingthreshold.
 3. The method for detecting defect signals according to claim1, wherein the defect flag signal is triggered to be at the first logiclevel when a third number of a plurality of the pts whose pit lengthsare bigger than a maximum value of the default pit length range reachesa second corresponding threshold.
 4. The method for detecting defectsignals according to claim 1, wherein the defect flag signal istriggered to be at the first logic level when a forth number of aplurality of pits whose the pit lengths smaller than a minimum value ofthe default pit length range reaches a third corresponding threshold. 5.The method for detecting defect signals according to claim 1, furthercomprising setting a maximum threshold, and triggering the defect flagsignal to be at the first logic level when a length of one of aplurality of the pits is bigger than the maximum threshold, wherein themaximum threshold is outside the default pit length range.
 6. The methodfor detecting defect signals according to claim 1, wherein all of thenumbers are reset when the defect flag signal is triggered.
 7. Themethod for detecting defect signals according to claim 1, wherein themethod is adopted in any of the group consisting of CD-ROM, CD-RW,DVD-ROM, DVD-RW, DVD+RW, and DVD-RAM.
 8. The method for detecting defectsignals according to claim 1, wherein the data signal is processed in 8to 14 modulation.
 9. The method for detecting defect signals accordingto claim 1, wherein the data signal is processed in 8 to 16 modulation.10. The method for detecting defect signals according to claim 1,wherein the default pit length range is from 3T to 11T.
 11. The methodfor detecting defect signals according to claim 1, wherein the datasignal is 588T.
 12. The method for detecting defect signals according toclaim 1, wherein the data signal is 1488T.
 13. An apparatus fordetecting defect signals, comprising: a buffering memory to receive adata signal, wherein the data signal includes a plurality of pits; afirst counter, connecting the buffering memory, to count a pit length ofone of a plurality of the pits in accordance with an order of aplurality of the pits; a second counter, connecting the first counter,to accumulate a first number of a plurality of the pits whose pitlengths are within a default pit length range, and compare the firstnumber with a first corresponding default threshold; a plurality ofthird counters, connecting the first counter, to accumulate a secondnumber of a plurality of the pits whose pit lengths are outside thedefault pit length range, wherein each of a plurality of the thirdcounters includes a corresponding pit length range to accumulate a thirdnumber of a plurality of the pits whose pit lengths are within thecorresponding pit length range respectively and compare the third numberwith a second corresponding threshold respectively; and a defect flagsignal generating circuit, connecting the buffering memory, the secondcounter, and a plurality of the third counters, to generate a defectflag signal at a default logic level, and trigger a logic level of thedefect flag signal to be at a first logic level or a second logic levelin accordance with a result of comparison of the first and the secondaccumulated numbers and the first corresponding and the second thresholdcorresponding thresholds, wherein the default logic level is the firstlogic level.
 14. The apparatus for detecting defect signals according toclaim 13, wherein the defect flag signal is triggered to be at thesecond logic level when first number reaches the first correspondingdefault threshold.
 15. The apparatus for detecting defect signalsaccording to claim 13, wherein a plurality of the third counterscomprising: a forth counter to accumulate a plurality of forth numbersof a plurality of the pits whose pit lengths are bigger than a maximumvalue of the default pit length range and smaller than a maximumthreshold, wherein the maximum threshold is outside the default pitlength range; a fifth counter to accumulate a plurality of fifth numbersof a plurality of the pits whose pit lengths are smaller than theminimum value of the default pit length range; a sixth counter toaccumulate a plurality of sixth numbers of a plurality of the pits whosepit lengths are bigger than the maximum threshold;
 16. The apparatus fordetecting defect signals according to claim 15, wherein the defect flagsignal is triggered to be at the first logic level when the forth numberreaches the corresponding default threshold of the forth counter. 17.The apparatus for detecting defect signals according to claim 15,wherein the defect flag signal is triggered to be at the second logiclevel when the sixth number reaches the corresponding default thresholdof the fifth counter.
 18. The apparatus for detecting defect signalsaccording to claim 15, wherein the defect flag signal is triggered to beat the second logic level when a plurality of the pits whose pit lengthsare bigger than the maximum threshold.
 19. The apparatus for detectingdefect signals according to claim 13, wherein the apparatus is adoptedin any of the group consisting of CD-ROM, CD-RW, DVD-ROM, DVD-RW,DVD+RW, and DVD-RAM.
 20. The apparatus for detecting defect signalsaccording to claim 13, wherein the default pit length range is from 3Tto 11T.